Assessing the impact of mode effects on survey estimates has become a crucial question due to the increasing appeal of mixed-mode designs. Despite the advantages of a mixed-mode design such as lower costs and increased coverage, there is sufficient evidence that mode affects may sometimes be large relative to the precision. They may lead to incomparable statistics in time or over population subgroups and they may increase bias. Adaptive survey designs offer a flexible mathematical framework to obtain the optimal balance between survey quality and costs. In this paper we employ adaptive designs in order to minimize mode effects. We illustrate our optimization model by means of a case study on the Dutch Labour Force Survey.